Orienting to face stimuli is a skill that emerges in the first year of life and that continues to develop over time. Failure to detect or respond to faces i one of the earliest hallmarks and predictors of autism spectrum disorder (ASD). Disruption in the early instantiation of the social brain networks results in lifelong social communication impairments in ASD. These social impairments in ASD are due, in part, to atypical eye gaze (findings from eye tracking studies) and abnormal neural activity when viewing faces (findings from electroencephalography (EEG) and magnetoencephalography (MEG) studies), with eye-gaze and face-sensitive neural measures considered potential ASD endophenotypes. Findings from these studies show that the brain changes associated with ASD precede clinical behavioral symptoms. Given a relatively late formal diagnosis around three years of age, interventions do not begin until significant early brain development is complete. So that interventions can start early there is a need for markers identifying individuals at risk for ASD. Although the above EEG/MEG endophenotypes are promising, our understanding is poor regarding how neural measures change as a function of development. To address this gap in the research, this K01 aims to examine the development of face-related neural processes in order to identify age-appropriate neural endophenotypes in young children with ASD. The proposed study is possible with the recent installation of a whole-head infant and young child MEG system at the Children's Hospital of Philadelphia (CHOP), and given a strong technical and clinical training environment at CHOP. MEG provides ideal brain measures in infants and young children due to minimal preparation time and given excellent temporal and good spatial resolution. For the K01 research project, a longitudinal design is employed to examine the maturation of the face-sensitive activity in fusiform face area and associated local and whole-brain neural networks in typically developing (TD) children aged six months to four-years-old (images of faces and houses passively viewed), with follow-up assessments every 12 months. Obtaining eye-tracking and MEG data from three and four-year-old children with ASD allows assessment of TD versus ASD differences in eye-gaze and face neural networks, and thus age-sensitive endophenotypes in children recently diagnosed with ASD. K01 findings will set the stage for a R01 examining eye tracking and neural activity in infants at-risk for ASD. K01 training will provide the tools and experience needed for K01 applicant Dr. Chen to become an independent developmental neuroscience researcher with a line or research focused on studying social cognition in infants and children with neurodevelopmental disorders. Training includes one-to-one mentorship (mentor Dr. Roberts and his team) in infant MEG as well as advanced digital signal processing. Clinical training at CHOP's Center of Autism Research (CAR) includes obtaining a better understanding of autism in infants and young children via work with developmental pediatrician K01 co-mentor Dr. Susan Levy, obtaining an in- depth theoretical background of ASD social processing impairments via mentorship from K01 advisor Dr. Roberts Schultz, and an understanding of ASD clinical and cognitive measures via observation, case conferences, and workshops with clinical psychologist K01 advisor Dr. Judith Miller. Training in developmental neuroscience is accomplished via classroom work and one-on-one mentorship with K01 consultant Dr. Hirsh- Pasek. Finally, training in eye-tracking is accomplished via classroom work and mentorship from K01 consultant Dr. Julia Stephen (experienced in eye tracking + MEG data collection and analyses). Building upon Dr. Chen's previous MEG experience and her growing experience in clinical imaging research, Dr. Chen is well poised to benefit from advanced clinical and technical training in order to develop a research program that uses brain imaging to understand the neurophysiological development of social cognition skills in TD infants and children as well as abnormalities in these processes in infants and children with ASD.